The vulnerability allows an attacker to cause a denial of service by sending an invalid U-format frame to a device running the Hitachi Energy RTU500 series CMU firmware that has IEC 60870-5-104 bi‑directional functionality enabled. The fault occurs during frame reception, leading to an indefinite hang or reset of the communication stack. This weakness is categorized as CWE‑184 and carries a CVSS score of 8.7, indicating a high severity.

This defect affects the Hitachi Energy RTU500 series CMU firmware used in RTU520, RTU530, RTU540, and RTU560 devices. All models running firmware version 13.8.1 are known to be vulnerable, as are devices operating any prior firmware that includes the same vulnerable code path.

The likelihood of exploitation is reflected in an EPSS score of less than 1 %, suggesting that known exploitations are rare or limited. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, but the high CVSS still warrants remediation. An attacker would need network access to the IEC 60870-5-104 channel and the ability to transmit malformed frames; enabling secure communication per IEC 62351‑3 mitigates the risk but does not eliminate the vulnerability.